the issue is that OGG videos are not known natively to Alfresco. You will have to add them to the list of mime-types, so that it will be served with the appropriate one. If you don't add the mime-type it will be served as "application/octet-stream", with that content-type it will be saved rather than displayed.

Hope this helped,

MrWHO

PS: A quick search for "alfresco custom extensions mime-type" will give you a good hint on how to add the mime-type.